Generalized analysis-by-synthesis based on system identification

In this paper, we propose an approach to modify the input signal such that it can be coded more effectively within the generalized analysis-by-synthesis framework. Since most of the low-bit-rate speech coders are designed based on the human speech production mechanism, the perceived quality of the speech reconstructed in the decoder degrades seriously if the original input signal deviates from the pure speech. In order to alleviate this problem, we introduce a criterion which compromises the quantization error with the distortion incurred due to the modification. The coder-decoder (CODEC) characteristic is described in terms of a transfer matrix, and it is estimated according to the least squares criterion. In contrast to the conventional modification techniques, our approach can be implemented as a simple front-end for any analysis-by-synthesis type coders. The proposed approach is found effective in reducing audible distortions through a number of listening tests.